Image guided surgical navigation is the process of planning minimally invasive surgical approaches and guiding surgical tools towards targets inside a patient's body with the help of anatomical imaging information obtained with techniques such as ultrasound, magnetic resonance, and various radiographic techniques. Such anatomical imaging information is useful because during a minimally invasive procedure, the surgical tools and the subcutaneous anatomy are not directly visible to the surgeon. With early image guided surgical techniques, the surgeon had to rely on her ability to accurately correlate two-dimensional slice-plane data with the three dimensionality of the patient in order to safely guide tools in the surgical field. The main drawbacks with this method were that it required abstract visualization by the surgeon in an attempt to develop an accurate mental picture of the interior anatomy, and that it did not provide feedback to the surgeon about the position of the surgical instruments during a procedure. These problems were addressed with the advent of frameless stereotactic systems, as disclosed in U.S. Pat. No. 5,230,623 to Guthrie (1993), U.S. Pat. No. 5,531,227 to Schneider (1996), U.S. Pat. No. 5,617,857 to Chader (1997), and U.S. Pat. No. 5,920,395 to Schulz which could locate and display the real time global position of a surgical instrument relative to reconstructed computer graphical models of diagnostic imaging data obtained through newer techniques such as computed tomography, magnetic resonance imaging, positron emission tomography, ultrasound scans, and other techniques. The methods of frameless stereotaxy were further improved by methods which could provide real time virtual anatomical views from the viewpoint of the surgical instrument as it was positioned inside the patient, as disclosed in U.S. Pat. No. 6,167,296 (2000) and U.S. Pat. No. 6,442,417 (2002) to Shahidi.
The backbone of minimally invasive surgical procedures is the endoscope, which affords surgeons an actual view of the internal anatomy. The combination of endoscopy and image guided surgery is interesting because it brings together the interior view of the endoscope and the exterior perspective of the image guided surgical system, much like local visual information such as landmarks or street signs are correlated with a map or a global positioning system to accurately determine position in a landscape. This combination is suggested by Shahidi, who teaches correlating and overlaying real endoscopic images with virtual images of the same view reconstructed from global imaging data, affording advantages such as graphical image enhancement. Shahidi exclusively deals with images generated from the viewpoint of an endoscope or surgical instrument looking along its longitudinal axis, tying the disclosure to fixed-axis instruments. Disclosure U.S. Pat. No. 6,442,417 specifically teaches the use of virtual perspective images of regions outside the field of view of fixed-angle endoscope as substitutes for obtaining live endoscopic views of such regions. Variable direction of view endoscopes can provide real images of such areas without the need for much shaft movement or reinsertion of the endoscope from an alternate direction. Variable direction of view endoscopes, which can be either rigid or flexible, as disclosed in U.S. Pat. No. 3,880,148 to Kanehira (1975), U.S. Pat. No. 4,697,577 to Forkner (1987), U.S. Pat. No. 6,371,909 to Hoeg (2002), WIPO publication WO 01/22865A1 to Ramsbottom (2001), DE 29907430 to Schich (1999), U.S. Pat. No. 3,572,325 to Bazell et al. (1971), and U.S. Pat. No. 6,007,484 to Thompson (1999) typically have a mechanism at the tip allowing the user to change the viewing direction without moving the endoscope shaft. Electronic endoscopes, as disclosed in U.S. Pat. No. 5,954,634 to Igarashi (1998) and U.S. Pat. No. 5,313,306 to Kuban, et al. (1994), with extreme wide angle lenses that allow the user to selectively look at portions of the optical field also belong to the class of variable direction of view endoscopes.
The value of using image guidance system in conjunction with variable direction of view endoscopy is potentially much greater than for standard fixed-angle endoscopy. Firstly, such a combination would allow real and virtual image correlation over a much greater viewing range, which would mean improved approach planning, improved guidance capabilities, and improved procedures overall. Secondly, it would provide a significant betterment of viewing navigation with variable direction of view endoscopes. A problem introduced by variable direction of view endoscopes is that it is difficult for the surgeon to estimate the changing endoscopic line of sight, which has a variable relationship to the shaft axis, because the tip of the instrument is concealed during use. Getting an external estimate of where the endoscope is “looking” during a procedure is important as the surgeon tries to integrate preexisting knowledge of the anatomy with the viewing process. Even with indicator knobs and dials (as in United States patent application 20020099263), or markers along the imaging axis (U.S. Pat. No. 6,500,115 to Krattiger et al.) it can be difficult to estimate which part of the anatomy is being seen through the endoscope because the user does not know the location of endoscope tip, which is the point of origin for the variable view vector. Fixed-angle endoscopes do not suffer from this problem to the same degree because the viewing direction has a fixed relationship to the endoscope shaft and can often be mentally extrapolated by the surgeon during a procedure.
The solution to this problem is to use an image guided system to provide the surgeon with a global perspective of the endoscope's viewing direction. In order to achieve this, it is not sufficient to simply monitor the position of the shaft of the endoscope as described in the prior art and done in current practice. The endoscopic viewing direction has to monitored as well. One way to do this, is to equip the view changing mechanism with an emitter/transponder which can be sensed through the patient's skin by external sensors. A better way to monitor the viewing direction is to sense its orientation relative to the endoscope shaft which position can be found by current image guided systems. This requires a variable direction endoscope instrumented with means to monitor its internal configuration. By combining the instrument's internal configuration data with its global position data as determined by the image guided surgical system, its viewing direction can then be determined. The variable direction of view endoscopes disclosed in the prior art listed above, are not equipped with means of monitoring their internal configuration. Apparently the only system currently capable of such internal configuration monitoring is the system disclosed in U.S. Pat. No. 6,663,559 by Hale et al. which discloses a novel system and method for precision control of variable direction of view endoscopes, making it ideal for integration with an image guided surgical system.
With proper integration, the extended viewing capabilities of an appropriately instrumented variable direction of view endoscope such as the one disclosed by Hale, combined with the features of an image guided surgical system could simplify and improve surgical planning and procedure. Global view vector monitoring would solve many of the endoscopic orientation problems surgeons face during variable direction of view endoscopy. Further, such an omnidirectional viewing navigation system could greatly expand the graphical image enhancement techniques disclosed by Shahidi.
From the discussion above, it should become apparent that there is a need for a method which provides the following capabilities: improved endoscopic orientation capabilities, global monitoring of endoscopic position and viewing direction, and improved surgical approach and procedure planning.